Hi eanreihan,
Welcome to Apple Support Communities. We understand that you're having an issue with your Wi-Fi connection when on a call on your MacBook Air. We'd like to help.
Just to confirm, are you also having issues with the audio? You mentioned it possibly being a problem with the mic so we wanted to be sure. Then, do you notice this when using FaceTime? How about when you're on another Wi-Fi network?
Let's have you start to create a new user account to see if it happens there. This will help us determine if it is system-wide or user specific. Create the account with these steps: Set up users, guests, and groups on Mac
If it continues, booting into safe mode can help: How to use safe mode on your Mac
Let us know how that goes.